# Can dark matter/energy disobey special relativity?

Loren Booda
Does the nonelectromagnetic property for dark matter/energy infer violation of the speed limit c or of inertial frame physics invarience? By disengaging themselves from light, I am assuming that dark carriers also free themselves from some constraints of the Lorentz transformations.

## Answers and Replies

Science Advisor
I'm not entirely certain what you said, I'm often not -
which is my fault of course...

But, if I'm not mistaken dark matter is actually
dictated by relativity (to keep galaxies stable as
they are) so I guess that if it exists and in more
or less the way it is assumed to exist, then it
probably obeys GR (both due to the above reason and
simply because GR appears to work, so far) and hence,
I guess - SR too.

I am not quite certain what you mean by implying that
neutral matter should get itself rid of some Lorentz
transformations from SR. It may get rid of electromagnetics
related transformations if its neutral but so do neutrons,
for example, how is that supposed to result in a violation
of SR ?

(If I totally missed something, feel free not to
bother with me. )

Live long and prosper.

Staff Emeritus
Gold Member
Dearly Missed
Loren, I think you misunderstand the relation of light to relativity. Because we always talk about the invariance of the speed of light, and because c comes into the Lorentz transformations and all, it's easy to conclude that "relativity is based on light" and that consequently something that doesn't couple to light isn't constrained by relativity.

But this is not so. Instead of light, it is the invariant speed c that is built into relativity. If you are going to have a spacetime, you have to have your time expressed in the same units as your space. To do that you will have to multiply your time units by a conversion factor: so many space units for each time unit. But that's a speed; Distance divided by time. Call the speed c. It's a time-space conversion factor.

Then work through the Lorentz transformations and see that c is invariant in all frames, or in other words every inertial observer will see the same speed c. Another consequence of the Lorentz transformations is that any particle with mass zero will travel at c. Such as photons, the hypothesized gravitons, and gluons inside the proton.

Of all of these, the photon is the most obvious to us because we have evolved to be highly visual animals. So we call c the speed of light. But relativity doesn't depend on there being light. Intelligent black holes could go through Einstein's operational definitions of relativity using gravitons. They would call c the speed of gravity (which it is).

Science Advisor
Gold Member
1) what's this got to do with QFT?

2) I assume by dark matter you are referring to the non-baryonic portion of the dark mass and there's no reason to think that it won't obey relativity.

PRodQuanta
I may be wrong, but isn't dark matter/energy undetectable. And if it is undetectable, how can it have properties. Maybe hypothetically it can though. I don't know, maybe I'm way off base, but check this out, here's where I got my assumption: http://www.nature.com/nsu/030707/030707-2.html
Paden Roder

Science Advisor
Originally posted by PRodQuanta
I may be wrong, but isn't dark matter/energy undetectable. And if it is undetectable, how can it have properties.

Dark matter is undetectable ONLY if it is composed of the "super-WIMPs" the artical mentions. So the research remains usefull, even if it detects nothing, because it will help support the super-WIMPs model of dark matter. But keep in mind that anything that we don't see constitutes dark matter. Planets, asteroids, dust, it all has mass and we can see very little of it (probably).

And even in the case of super-WIMPs, we should remember that "undetectable" onyl means really really hard to detect, and not absolutely undectable. If an object is truly undetectable, and has no properties, then it also cannot be called an object, nor said to exist. Dark matter has mass and exerts a gravitational pull, so I think it must obey SR. If it doesn't, then there's a whole new field of physics out there that hasn't even been guessed at.

Loren Booda
drag et al,

Better consider selfAdjoint's explanation than mine.

Loren Booda
jcsd,
1) what's this got to do with QFT?
where would you have put it, given the options?

Staff Emeritus
Science Advisor
Gold Member
"Dark matter" and "dark energy" are used to refer to two different things.

Originally "dark matter" was kinda like bookkeeping - a variety of astronomical observations seemed to show there was more mass, in various places, than could be accounted for by the observed (or inferred) stars, dust, and gas. So the rest was "missing mass".

Then cosmology started to grow up as an observational science, and modellers put in various amounts of 'dark matter' - sometimes 'cold', sometimes 'hot', and occassionally 'warm' - to make their toy universes look vaguely realistic after 10-15 billion years.

It wasn't long before the "missing mass" became 'dark matter'.

Fast forward some more years. Some of the missing mass isn't (better observations showed everything present and correct), some much better understood (3D distribution, total mass, etc), and some remains mysterious. The toy universes grew up too.

Some particularly good progress has been made with dark matter in galaxy clusters - gravitational lensing and X-ray observations of the hot intra-cluster gas (with various assumptions about thermal equilibrium) give some nice dark matter distributions.

Key assumption? That the dark matter interacts gravitationally with the visible matter.

Dark energy is a very different story.